What’s the difference between all those instances?
We have Lemmy.world, Lemmy.ml, beehaw.org, I think even yiffit.net.
If I log in using wefwef it asks me where I want to login. And when I make a new account using another instance, it says ”… Lemmy is federated, so you can interact with everything on lemmy.ml even if you’re registered on a different instance.“
So if I’m registered on lemmy.world, how can I interact with lemmy.ml?
Think of them as different email servers. It's all federated and connected. As long as you're looking at the "all" timeline it will show you posts from across every instance. And you can follow communities across instances. For example I'm on a different instance than you but I can see your post and comment on it. Just start subscribing to some. check out the list below for a couple migrated subreddits.
From what I’ve heard, only communities from other instances that users in your instance are subscribed to will show up. This is because (as far as I know) the instances only request data from other instances of what users have requested, and not a constant stream of updates that no one has a need for.
This means there is a slight advantage to being on a larger instance. Of course, you're gonna have to deal with a laggier experience as the server gets overloaded. If you don't mind using the lemmy explorer to hunt down the subs you want to subscribe to, it's a better experience.
I couldn't see the community I made on lemmy.world in lemm.ee until I searched for it multiple times until it finally showed up. So some users may believe the community they're searching for may not exist, even though it does on an another instance. Best to use Lemmy Explorer just in case when looking for a community.
I'm confident that "mailing lists" are not a thing most people will know about or understand today, and for a lot of people "email" and "gmail" are completely synonymous terms. A lot of people will have never interacted with an @yahoo account, I wasn't aware they were even still in business.
It is "just like email" in a sense you can send email from your gmail to someone using yahoo, hotmail or even their own self hosted server and it still gets delivered despite all those different servers. And that's where analogy of similarity to email ends.
I can (could) post to reddit with Boost, my friend uses Apolo, this other guy uses RIF. To the layman what's the difference between my instance, your instance, wefwef, jerboa, etc. The general public don't know about email servers any more than Lemmy instances.
The analogy isn't meant to reflect who receives the message, but how communication interacts.
Each lemmy/federated instance uses a prefix and a suffix to create a name. So for example, I'm Melpomene@kbin.social here, where Melpomene is me and kbin.social is where I reside. This is similar to email because it works similarly.... I might be Melpomene on Gmail, but my actual user name reflects both me (Melpomene) and the email instance I call home (gmail.com.)
If you want a specific analogy to messaging, though... when you send a message to a lemmy community, you're basically responding to a distribution list. nostupidquestions@lemmy.world is akin a distribution list, the distribution list is (technically) visible to anyone on the instance, so anyone can see the message. If you're on a federated instance that allows private messages, though, sending to an individual user would still function like email in that only the person messaged would see it.
Edit: The comparison is not exact, granted. It's meant to de-mystify the prefix/suffix format of federation, not to offer a one to one comparison to email.
Another way of looking at it is cross platform videogames where Kbin.social is playstation Lemmy.world is xbox and a third one would be Nintendo Switch. If the game has a chat feature what one person posts from xbox would appear for the playstation players and visa versa. Federating is basically when they first connect to each other to become multi platform.